Investments Investments (Schedule Of Amortized Cost and Fair Value of Available-for-sale Securities and Related OTTI Recognized in AOCI) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	$ 79,208	$ 77,835
Available-for-sale,Gross Unrealized Gain	981	1,528
Available-for-sale, Gross Unrealized Depreciation	(1,078)	(424)
Available for sale, Fair Value	79,111	78,939
Available for sale, OTTI recognized in AOCI	(5)	(6)
US Treasury and Government [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	3,893	3,701
Available-for-sale,Gross Unrealized Gain	22	32
Available-for-sale, Gross Unrealized Depreciation	(77)	(35)
Available for sale, Fair Value	3,838	3,698
Available for sale, OTTI recognized in AOCI	0	0
Foreign Government Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	21,705	20,514
Available-for-sale,Gross Unrealized Gain	513	622
Available-for-sale, Gross Unrealized Depreciation	(187)	(106)
Available for sale, Fair Value	22,031	21,030
Available for sale, OTTI recognized in AOCI	0	(1)
Corporate Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	23,509	23,453
Available-for-sale,Gross Unrealized Gain	332	638
Available-for-sale, Gross Unrealized Depreciation	(274)	(95)
Available for sale, Fair Value	23,567	23,996
Available for sale, OTTI recognized in AOCI	(4)	(4)
Collateralized Mortgage Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	16,116	15,279
Available-for-sale,Gross Unrealized Gain	53	111
Available-for-sale, Gross Unrealized Depreciation	(349)	(100)
Available for sale, Fair Value	15,820	15,290
Available for sale, OTTI recognized in AOCI	(1)	(1)
US States and Political Subdivisions Debt Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Available for sale, at amortized cost	13,985	14,888
Available-for-sale,Gross Unrealized Gain	61	125
Available-for-sale, Gross Unrealized Depreciation	(191)	(88)
Available for sale, Fair Value	13,855	14,925
Available for sale, OTTI recognized in AOCI	$ 0	$ 0

Accumulated other comprehensive loss related to portion of other than temporary impairment (OTTI) due to factors other than credit losses on debt securities categorized as available-for-sale that an entity does not intend to sell and which it is not more likely than not that the entity will be required to sell before recovery of the amortized cost basis of the debt security. The amount represented by this item is net of tax, as applicable.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 9A
-URI http://asc.fasb.org/extlink&oid=82896770&loc=SL6284427-111562

Reference 2: http://www.xbrl.org/2003/role/presentationRef
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Amount of debt securities categorized neither as held-to-maturity nor trading.

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